The present invention relates to a magnetic separation purifying apparatus intended for purification of water quality, solid-liquid separation, etc., and more particular, to a construction of a magnetic separation purifying apparatus capable of favorably separating a magnetic substance irrespective of fluctuation of a water surface in a magnetic separation part and stably discharging a high density sludge in trapping of the magnetic substance and magnetic separation of a trapped substance with a membrane.
Intended for solid-liquid separation, etc. is a magnetic separation purifying apparatus, in which a thin wire net, a net knitted from polymeric fiber, and a film are used as a water separation membrane, a coagulant and magnetic powder are added to raw water containing polluted particles (called sludge) to generate magnetic flocs, the magnetic flocs are separated by the membrane, and the magnetic flocs collected by the membrane is magnetically separated and removed by magnetic field generating means, and a high concentration sludge is recovered. The construction is described in, for example, JP-A-2002-273261. The membrane separation purifying apparatus comprises a net formed from thin wire of stainless steel, polymeric fiber, etc. and having mesh size of, for example, several tens of micron meters. In order to separate a minute polluted substance smaller than a projected area or a projected diameter of the net, a coagulant such as aluminum sulfate, poly aluminum chloride, and poly iron sulfate, and magnetic powder are beforehand added to raw water to be agitated to form magnetic flocs, in which the coagulant joins minute solid suspended matters, alga, fungus, and microorganism in the raw water and which has a magnitude of several hundreds of micron meters. Such magnetic flocs cannot pass through the membrane, of which mesh size is several tens of micron meters, but is caught and separated at a high extraction ratio, and water having permeated the membrane makes a purified water of high water quality.
After the magnetic flocs collected on the membrane is washed away from the membrane by a wash water, magnetic flocs staying in the vicinity of a water surface is attracted and magnetically separated by a magnetic force of a magnet, which is made stationary and arranged in the vicinity of the water surface, and transported and removed into a sludge recovery tank by sludge transport means.
Finally, sludge is normally conveyed to a disposal site or an incineration plant by a truck to be composted.
JP-B2-3228430 describes a sewage disposal apparatus, in which magnetic powder in sewage having flowed into a sewage disposal tank is attracted and separated from the sewage by a magnetic plate arranged in the sewage disposal tank to be discharged outside the sewage disposal tank. The sewage disposal apparatus comprises: the sewage disposal tank provided at a lower portion thereof with a sewage inflow port and at an upper portion thereof with an exhaust port for water to be processed; a plurality of disk-shaped magnetic bodies immersed and arranged in sewage in the sewage disposal tank and aligned and mounted on a rotating shaft at predetermined intervals; a plurality of permanent magnet pieces mounted on surfaces of the respective disk-shaped magnetic bodies and arranged so that opposed magnetic poles are different from each other between opposed disk-shaped magnetic bodies; a scraping device composed of an endless belt with scrapers and going around to scrape sludge attracted to surfaces of the permanent magnet pieces and to move the scraped sludge to above the disk-shaped magnetic bodies; a sludge discharge passage provided in sewage in the sewage disposal tank to surround the scraping device to guide that sludge, which is scraped by the scraper, to a sludge discharge port; and an overflow port formed in communication with the sludge discharge passage to permit the water to be processed in the sludge discharge passage to overflow.
JP-A-2002-79353 describes a rotating drum type magnetic separation apparatus comprising an inner cylinder housed in a rotating drum made of a non-magnetic material and arranging magnets in desired positions on an outer peripheral surface thereof, and a squeezing roller and a scraper, which abut against the rotating drum, the rotating drum having the whole or desired portions of a surface thereof magnetized at a desired depth.
As described above, the prior art involves a problem that since the magnetic flocs washed away from the membrane and staying in the vicinity of a water surface is magnetically attracted by a stationary magnetic field distribution of a stationary magnet, the capacity of removing many magnetic flocs present in the vicinity of the water surface is lowered, magnetic flocs in the water to be processed are heightened in density, the purifying rate by the membrane is decreased, and the purifying capacity is lowered in the case where the water surface fluctuates up and down and a magnetic force at the water surface is in a weak level.
On the other hand, in the case where sludge is conveyed to a disposal site or an incineration plant by a truck and in the case where sludge is composted, sludge must be decreased in water content prior to conveyance and compost treatment so as to make the water content about 85% for prevention of leakage of the water from the sludge at the time of transportation and to make the water content about 75% for activation of microorganism, which decomposes an organic matter at the time of compost.
Here, there is caused a problem that when the purifying rate by the membrane is decreased and a water surface of the water to be processed rises, the water to be processed containing magnetic flocs overflows into a sludge recovery tank, which is disposed adjacent to the filtering water tank to magnetically separate, remove and recover magnetic flocs as a high concentration sludge, and the sludge recovered at high concentration is considerably diluted with the inflowing water to be processed to become low in concentration to be considerably increased in volume, thus resulting in an increase in dehydration cost when the water content is made small.